1. Field of the Invention
The present invention relates to a cable apparatus for supplying power from an electronic apparatus to another electronic apparatus, and more particularly, to a cable apparatus for use in connecting a personal computer (will be referred to simply as "PC" hereinafter) to it associated peripheral devices.
2. Description of the Related Art
Generally, the computer system of a PC is configured such that the PC and its associated peripheral devices are connected to each other by a cable apparatus such as a power line via an interface for each of the peripheral devices. The computer system uses a display, keyboard, mouse, printer, modem, etc. as the peripheral devices. Recently, the video camera, electronic still camera and the like have been added to the above-mentioned PC-oriented peripheral devices. Namely, more and more kinds of peripheral devices are used with a PC.
The cable apparatus comprises a cable and a plug connected integrally to either end of the cable. It serves as a transmission path to convey a power and the like from a PC to each peripheral device.
For connection between the PC and each of its associated peripheral devices via the cable apparatus in a computer system, the PC is provided on its enclosure with many connecting terminals such as an analog RGB terminal, digital RGB terminal, etc.
Along with the increase in kind of the above-mentioned peripheral devices and improvement in PC performance in these years, cable apparatuses have been proposed for which plugs and receptacles have been standardized in shape as in the IEEE 1394 high-performance serial bus (will be referred to as "IEEE 1394" hereinafter) for connection of a variety of peripheral devices to a PC via a single interface.
The cable apparatus in conformity with the IEEE 1394 standard has been proposed for a compact design, lower cost, high versatility, etc. It comprises a cable having a power line, etc. and a small plug integrally secured to either end of the cable and having six terminals.
Namely, the cable apparatus conforming to the IEEE 1394 standard can connect power from a PC directly to its associated peripheral devices since it incorporates a power line.
Also, the interface according to the IEEE 1394 standard is characterized in that it can connect a plurality of peripheral devices to a PC and the cable can be connected to, and disconnected from, each of the peripheral devices while the latter is being energized and in operation, that is, in a hot status.
Next, a conventional cable apparatus will be described herebelow with reference to the accompanying drawings:
Referring now to FIG. 1, there is schematically illustrated in the fon-n of a block diagram a conventional cable apparatus adapted to supply both an internal power and an external power. Also, FIGS. 2A and 2B show schematic block diagrams of conventional cable apparatuses, one adapted to supply only an internal power (as in FIG. 2A) and the other adapted to supply only an external power (as in FIG. 2B).
In FIG. 1, the conventional cable apparatus is generally indicated with a reference 120. The cable apparatus 120 comprises a power supply unit 121, Schottky diode 122, fuses 123, 124 and 125, and connectors 126, 127 and 128.
In the cable apparatus 120, the connectors, 126, 127 and 127 should desirably have a high impedance in relation to each other so that they will not influence each other. To supply and receive an external power between these connectors in case no internal power is supplied but the external power is supplied, however, the cable apparatus 120 is constructed as shown in FIG. 1. To pass a current only when the internal power is supplied but no current when no internal power is supplied, the Schottky diode 122 is provided for each bus so that the power supply side works as an anode while each bus works as a cathode.
In the cable apparatus 120, the power supply unit 121 supplies an internal power as will be described below:
As shown in FIG. 1, the power supply unit 121 supplies an internal power through the Schottky diode 122 to the connector 126 via the fuse 123, connector 127 via the fuse 124, and to the connector 128 via the fuse 125, respectively.
Next, the power supply unit 121 which does not supply internal power, namely, in which an external power is supplied from the connectors, will be described below:
At least one (connector 126, 127, 128 for example) of the connectors 126 supplies the external power to the connector 127 via the fuses 123 and 124, and to the connector 128 via the fuse's 123 and 125, respectively.
The connectors 127 and 128 supply the external power to other connectors in the same manner as the connector 126. The external power may be supplied to more than one of the connectors 126 to 128. When no internal power is supplied, the connectors supply and receive an external power between them as in the above.
In FIG. 2A, the convention cable apparatus is generally indicated with a reference 130. The cable apparatus 130 comprises a power supply unit 131, fuse 132, Schottky diodes 133, 134 and 135, and connectors 136, 137 and 138.
In the cable apparatus 130, each of the connectors 136 to 138 has a higher impedance than the others. That is, the cable apparatus 130 is an ideal one in which an internal power can be supplied at a higher impedance at one of the connectors than the others.
In the cable apparatus 130, the power supply unit 131 supplies an internal power as will be described below:
As shown in FIG. 2A, the power supply unit 131 supplies an internal power to the connector 136 via the fuse 132 and Schottky diode 133, connector 137 via the fuse 132 and Schottky diode 134 and to the connector 138 via the fuse 132 and Schottky diode 135, respectively.
However, when the power supply unit 131 supplies no internal power but an external power is supplied at the connectors 136, 137 and 138, the power will not flow from the connectors 136, 137 and 138 to the fuse 132 because of the Schottky diodes 133, 134 and 135, so that the connectors 136, 137 and 138 cannot supply and receive the external power between them.
Therefore, in the cable apparatus 130, the connectors cannot supply any external power to one another.
Finally, a cable apparatus having no internal power source, namely, in which an external power is supplied from the connectors of the cable apparatus, will be described below:
In FIG. 2B, the conventional cable apparatus is generally indicated with a reference 140. The cable apparatus 140 comprises fuses 141 and 142 and connectors 143, 144 and 145.
In this conventional cable apparatus 140, at least one (connector 143 for example) of the connectors 143 to 145 can supply an external power to the connector 144 via the fuse 141, and to the connector 145 via the fuses 141 and 142, as shown in FIG. 2B.
The connectors 144 and 145 supply the external power to other connectors in the same manner as the connector 143. The external power may be supplied to more than one of the connectors 143 to 145. Thus in this cable apparatus 140, no internal power can be supplied but the connectors 144 to 145 can supply and receive an external power between them.
Since in the cable apparatus 140, the connectors 143 to 145 are connected to each other by means of fuses 141 and 142, respectively, when an external power is supplied to the connectors 143, 144 and 145, it can be supplied and received between the connectors and delivered from them to outside.
However, the conventional cable apparatuses do not strictly meet the requirements for power supply prescribed in the interface standard. In many of the conventional cable apparatuses, priority is given to reception of an external power. Thus, the conventional cable apparatuses are disadvantageous in that when an internal power is supplied, each bus will not have a high impedance in relation to each other.
Also, in the conventional cable apparatuses, the setting of power class conforming to the requirements in the IEEE 1394 standard are not automatically changed but the user has to change the setting using a switch on the keyboard or using GUI, a command or the like. Thus, failure to change a power class setting results in setting of a power class for supply of an external power or setting of quite a different power class setting from a required one.